Compressed gas containers for the storage and distribution of ultra-pure gases are produced from stainless, high-alloy chrome-nickel steels. As a rule these are compressed gas bottles having a volume ranging from 5 to 50 liters which are produced as a welded construction from a cylindrical pipe which is seamless or has a longitudinally welded seam. This pipe is closed off by two welded-on caps. Before welding, the inside surfaces of the parts are easily accessible and can be subjected to the mechanical pretreatment for the necessary degree of roughness required for the subsequent surface quality. The quality of the inside surfaces of containers made of such high-alloy chrome-nickel steels must guarantee that the purity and composition of the contacting gases are not influenced so that it must be possible to electrolytically polish these surfaces. In conventional compressed gas bottles, the threaded opening for the valve connection is the only access to the inside of the container. As a result, electrolytic polishing becomes very difficult and, in particular, for large volume bottles requires high expenditure.
Another problem results from the use of high-alloy chrome-nickel steels as container material. Since these materials have a very low strength, compressed gas containers made from these materials must be cryodeformed.
In this process, the prefabricated container is cooled to very low temperatures and is plastically deformed as a result of internal pressure until the container material has reached the strength required for the later application.
Since a subsequent heat treatment again cancels out the strength increase produced by the cryodeformation, all welding work required for the production of the container must have been completed before the cryodeformation. This relates, in particular, to the welding-in of the valve socket for the accommodation of the gas bottle valve in the upper cap and possibly the formation of the base of the bottle near the lower cap.
Unlike for conventionally produced compressed gas containers, very special demands are made for cryodeformed containers on the container closure. The closure must resist the high internal pressure at cryogenic temperatures required for cryostretching and in this process should not lose its absolute sealing function.